Many intercellular signaling events in both vertebrates and in Drosophila have been shown to require one class of cell surface proteins, the heparan sulphate proteoglycans (HSPG's). HSPG's are proteins with attached chains of modified sugars polymers, called heparan sulphate (HS). Both the core proteins and the HS chains of HSPG's have been shown to be important for many signaling events. The goals of this proposal are to 1) identify null mutants in the Drosophila dally gene, which encodes the core protein of a glypican-like HSPG 2) identify suppressors and enhancers of daily that will yield mutations in the HS synthetic enzymes as well as other modifiers, and 3) ascertain the role that each of the identified Drosophila O-sulphotransferases (OST) plays in developmental signaling using RNA interference. Several genetic and molecular assays will be used to determine if a particular mutation or reduction of one of the OST's affects the Wingless, Hedgehog, FGF, or Decapentaplegic signaling pathways. These studies will greatly expand our understanding of the roles of HSPG's in signaling and development.